Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.Department of Tropical Medicine, School of Public Health and Tropical Medicine, Tulane University, New Orleans, LA 70112, USA.

Mother knows best

Dynamic natural environments are challenging places to start life. In many species, however, the environment the mother lives in can actually shape the environment in which her offspring grow. Such maternal effects facilitate the exchange of important environmental information across generations. Duckworth et al. show that a mother's physiological responses to her environment can convey more complex information than we thought (see the Perspective by Dantzer). Female western bluebirds deposit more androgens in their eggs when competition for nest sites increases. This results in more-aggressive male chicks that are more likely to move on and colonize new, less crowded habitats.

Abstract

An important question in ecology is how mechanistic processes occurring among individuals drive large-scale patterns of community formation and change. Here we show that in two species of bluebirds, cycles of replacement of one by the other emerge as an indirect consequence of maternal influence on offspring behavior in response to local resource availability. Sampling across broad temporal and spatial scales, we found that western bluebirds, the more competitive species, bias the birth order of offspring by sex in a way that influences offspring aggression and dispersal, setting the stage for rapid increases in population density that ultimately result in the replacement of their sister species. Our results provide insight into how predictable community dynamics can occur despite the contingency of local behavioral interactions.